Reader 10.1 is a full Reader installer (.msi or .exe) - not a Patch (.msp) and cannot display the error you mentioned.
Are you sure you are updating Reader and not Acrobat?
Are you using Updater or downloaded update from somewhere?
If you can provide as much information as possible, someone will be able to help you.
What is at that link then if not a patch?
This one is for a special Reader called MUI. This Reader has an ability to install multiple language files.
If you have it, you should use this patch.
Most people have simple versions of Reader and this patch will not work for them.
Tricky, OK. It just looked to me like patch upgrade that would handle multiple languages of Reader. Looking back, I see that the one I used to patch 10.0 to 10.01 didn't have "MUI" in the title.
So, is there any non-MUI version patch for Adobe Reader?
I also cannot apply msp patch file for my box. I wonder why only MUI patch is there...
10.1 Reader patch is available only for MUI Reader.
However,full Reader installers for 10.1 are available for MUI as well as normal,non-MUI, Reader.
You may use following links to download 10.1 Reader.
MUI Full Reader 10.1 :
Full Reader 10.1http://www.adobe.com/support/downloads/detail.jsp?ftpID=5138